Many different methods have been proposed, tested and applied for drawing off filaments (thread). Among the other methods are air and vapor streams (jets), ejectors placed transversely to the direction of emerging filaments and centrifuging disks. It is important to draw the filaments safely such that they have a relatively constant diameter before their distribution into fibers. The drum-draw-off process was proven to be the safest in which the filaments drawn from nozzles of a nozzle bushing containing the liquid glass run upon a drawing drum and from this are carried along over a portion of its circumference and are lifted before a reaching a single turn and are distributed into a staple fiber. It is possible to set and maintain the peripheral velocity according to a precise ratio of the diameter and r.p.m. of the drum which enables maintenance of a determined diameter of the filament within very narrow tolerances. For many years, diameters of drums of 1000 mm and lengths of drums of 1000 mm, as well as draw-off speed of about 50 m/sec have been conventionally adopted. When the drawn-off filaments are removed from the drum (lifted) by a shedder (stripping device) before the termination of a sole circle around, divided into fibers, which are then guided by a deflection to a conveyor belt and led through it by a circulatory draft created by rotation of the drum, the process is designated as a "dry process", which is contrary to a "wet process" in which the glass threads cut into bundles of an equal but relative short length, suspended in water, are filtered out so as to form fleece on a forming wire. The advantage of the wet process and the reason for its increased application, compared to the dry process, lies in its high productivity. This consists, among others, in that in this process, at an other point, glass strands are produced in large amounts, for example by winding on drawing drums the wound up portions are removed as "fleece" and cut into fibers which can then be poured into water tubs (tanks) (U.S. Pat. No. 3,766,003). However, the market also requires fleeces having greater fiber length since these do not need such a strong binder which also leads to softer and more flexible fleeces.
Problems arise in the dry process. Among others, exact revolution of the heavy drum requires precise drum seating which means that the surface of the drum must be kept painfully, clean and smooth. Despite such problems with the drum, the biggest problem lies with the shedder (stripper). German Pat. No. 1,285,114 describes the problems connected with application of a shedder. The departure from previously used thick scrapers and the turning to extremely thin elastic shedders, amounted at the time to great progress. Problems connected with shedders are of an alternating effect with those of the draw-off or spinning drum, in addition with those caused by the so called "condensation of threads" problem which condensation has increased enormously during the last ten years. This dramatic increase has made it more diffcult, in effect, overloading the draw-off method of the drum. It originally started with 100 to 150 filaments produced by melting-off from the ends of in a series of arranged rods, drawn-off by a 1000 mm wide drum and lifted from it. Today we have arrived to 500 and more nozzle equipped bushings. This means that the same micron thick threads (filaments) lie together more tightly on the same width of drum, namely less than 1 mm today in comparison to about 1 cm before. As a result, guiding on the surface of the drum must be more precise and the filaments must not be laterally shifted during their partial winding around. In addition, the shedder must simultaneously safely lift and lead more filaments now. The surface of the drum must also be completely smooth, since grooves and channels are more damaging in that a smaller number of threads will ascend. This again means that the shedders must be replaced more often and the durms cleaned and replaced more often. The shedders (strippers), which not only have the task of lifting or removing the filaments from the surface of the drum but also deflecting the rotary draft created by rotation of the drum and transporting the formed filaments, must be applied only by a light pressure or without pressure against the surface of the drum, otherwise a substantial frictional heat will be created that stresses especially the edge of the shedder, necessitating its repointing and replacement more often.
The problems connected with increased density of the threads on the shedder set mechanical limits on economical glass fleece production. Also to a great extent, the changing deposits in the dry fleece installations, according to the German Pat. Nos. 976,682 and 1,270,456, working according to the drum process are worldwide proven and accepted, so that a stronger process has prevailed, similar to that used in the paper industry, the so called wet process. According to U.S. Pat. No. 3,766,003, problems connected with the removal of large numbers of filaments from the periphery of the drum arise when trying to run the filaments layerwise on the drawing drum and separate them as fleece only after obtaining a certain thickness of layer along a coat line of the drawing drum.
Accordingly, a task of the invention lies in being able to exploit the progress of the increased filament or thread density in the dry process and eliminate the problems connected with shedders or at least considerably reduce their significance, for example, by reducing system downtime associated with shedder problems.
It is known to collect into a filaments emerging from the nozzles of a muffle containing liquid glassinto strands, to cut the strand into pieces of equal length and to deposit the thus formed chopped strands as so called "chopped strand mat" on a forming wire. For this purpose it is necessary to provide the individual filaments with a binder, which filaments converge into a strand already very early on their way from their formation on the outlet of the nozzle until they are deposited, which takes care of their mutual cohesion in the strand. For example, British Pat. No. 785,935 describes a method in which individual filaments are led to a disk collecting them in a strand and notched on its periphery, after they have previously been sprayed in the so called "filament harp" by a binder. The filaments arrive about vertically from above into the coat notch of the disk and leave this disk horizontally as a strand, passing thus about 90.degree. of the disk forming the strand. The strand is removed from this disk by several subsequently placed ejectors which have to extend the individual filaments connected into a strand and draw it, in spite of the already sprayed on binder, to the desired diameter. Between two ejectors is a cutting mechanism which divides the strand into cuttings, and the last ejector brings and deposits these finally on a sieve wall. According to U.S. Pat. No. 3,318,746, it is known to collect the filaments with the help of several mutually distanced, notched rollers into strands so as to provide them with a binder just before they run through the first roller into about a six strands forming roller. After the second roller, the strands arrive over a stretching roller on the drawing disk which can apply then only a drawing-off effect on the strands and not extending drawing effect on the individual filaments, i.e. cannot draft them to a desired and a different diameter before they emerge from the muffle. From this drawing disk, the strands are lifted always as a whole unit forming a loop-shaped throw-off on a conveyor bank placed below the disk and lifted by a spoke wheel that reaches with its spokes through openings in the surface of the casing. On the other hand, in the dry process, the improvement of which is the purpose of the invention, the loose filaments not having been treated with binder are grouped into strands of collected filaments and drawn to the desired diameter by a rotating drawing surface and subsequently separated into individual fibers which are collected with circulating draft produced by the rotating surface.